On containers for liquids, such as e.g. metal cans or receptacles made from coated or laminated cardboard, for the purpose of a resealable opening and for easy pouring, use is often made of closure units, preferably made from plastic and comprising a pouring part with a pouring opening and a closure part closing the pouring opening of the pouring part and fitted into an opening of the container. Such a closure unit is e.g. disclosed by Swiss patent application 2740/91, which corresponds to U.S. Ser. No. 08/050,477.
Such closure units are made from plastic, which is inexpensive and has favorable characteristics for the manufacture of the closure unit. It enables manufacture to take place with tools so as to permit a considerable output. The aim is that the closure unit only insignificantly increases the container price and consequently the container with the closure unit appears attractive to the user from a maximum number of standpoints. However, it can occur that the product in the container has to be given additional protection against influences from the environment, so that it can be kept longer. Such influences which can unfavourably influence the product are e.g. environmental moisture and air, together with light or radiation of other types. It is also possible for gases, such as waste gases, which are mixed with the environmental air, to unfavorably influence foods in such containers and oxidize the vitamins contained therein or modify the taste of such foods. Therefore it can be desirable to provide such containers with coatings, which do not permit the passage of gases and/or light.
The closure unit must also satisfy the requirements generally made on the container. In this sense the procedure has hitherto been such that either the opening in the container or the opening in the closure unit is covered with a foil or film, which must be destroyed at the time of the initial pouring out or removal of the product.
The disadvantage of this solution is that said film or foil, has to be removed or perforated at the time of the initial pouring out and that it subsequently can no longer fulfil its intended function, i.e. it is for example no longer gas-tight or is no longer impervious to light. It can also no longer fulfil its function if a closure part of the closure unit again firmly closes the pouring opening, because on closing the closure part the film or foil is not restored to its original state. Therefore, the container as a whole, has lost part of its characteristics as a result of the initial opening of the closure unit in the same way as for a container not having a closure unit and is also accepted, because it would appear to be unavoidable.